As of today (May 10th 2006) each account has 2,722MB. This number continues to grow minute by minute.
Historical Information As of April 1st 2005, GMail accounts are being increased from 1,000 MB to 2,000 MB of storage.
said by the GMail Folks :
Storage is an important part of email, but that doesn't mean you should have to worry about it. To celebrate our one-year birthday, we're giving everyone one more gigabyte. But why stop the party there? Our plan is to continue growing your storage beyond 2GBs by giving you more space as we are able. We know that email will only become more important in people's lives, and we want Gmail to keep up with our users and their needs. From Gmail, you can expect more.
said by GMAIL FAQ:One gigabyte of storage means the average user can go five years without ever deleting a single message, so we don't expect you to get close to your quota anytime soon.
However, if your mailbox nears its storage quota, you'll see a warning message at the top of your inbox letting you know how much storage you have left. If you reach more than 90 percent of your storage quota, we'll also send a message to your alternate email address (if you've provided one) to let you know.
If you manage to go over your storage limit, Gmail will hold your messages for 10 days until you clear out some of your old messages to make way for new ones. If you don't delete anything within the allotted time, you won't be able to receive new messages and messages sent to your account will be returned to the sender